Preclinical studies indicate that soy-containing diets suppress the development of pain behaviors and hyperalgesia seen following nerve injury and recent data indicate a similar protective effect of a diet high in soy protein in inflammatory and bone cancer pain models. Very few studies have directly studied the effects of soy-containing diets on pain sensitivity in humans, but one recent randomized clinical trial suggests that dietary soy supplementation may reduce pain due to osteoarthritis. The proposed study will examine whether a soy protein supplement reduces the pain commonly experienced following thoracotomy for lung surgery. The growing recognition that greater acute pain leads to persistent pain following tissue healing underscores the importance of identifying viable strategies, including both non-pharmacological as well as pharmacological, for reducing the acute pain associated with surgery. Using a 2 group (soy protein supplementation vs. matched milk placebo supplementation) design, patients undergoing elective major open thoracotomy for lobectomy will be randomly assigned to one of these two treatment groups. Patients will begin taking the soy/placebo supplement 2-3 days prior to thoracotomy and continue daily consumption of the supplement for an additional 24 weeks. The feasibility/pilot study will examine the effects of soy supplementation on outcome measures during three post-operative time periods: 1) the immediate post-operative period;and 2) during 2-12 weeks following surgery. Pain is the primary outcome domain of interest in this pilot study and measures will include pain severity ratings and pain medication use. Function and quality of life are the secondary outcome domains of interest and measures will include pain-related interference with daily activities, sleep, and health-related quality of life. Outcome measures will be collected bi-weekly throughout the study. The study aims to determine the feasibility and acceptability of soy supplementation in the period surrounding thoracotomy, determine level of adherence to soy supplementation over the 3-month period of follow-up, and estimate the effect size of soy supplementation relative to placebo in reducing significant pain following thoracotomy. The proposed study will provide the necessary groundwork to move towards such a larger randomized trial to evaluate the pain-reducing effects of soy protein supplementation following thoracotomy. This study will examine whether a supplement that contains soy protein reduces the pain patients experience following a thoracotomy, a common surgical procedure for lung tumors. Study participants will be randomized to take either a soy protein or milk protein supplement 2-3 days prior to and for 3 months following surgery. The effect of soy on pain and use of pain medications will be determined, as well as the acceptability of the supplement to patients under these conditions.